Optical fiber amplifier, light source device, exposure device, object inspection device, and treatment device

ABSTRACT

A polarization state adjusting optical element is formed by a ½ wavelength plate and a ¼ wavelength plate and its polarization direction and elliptic degree are adjusted. By adjusting the polarization state adjusting optical element in advance, even if the output of a pump light source is changed, the polarization characteristic (polarization direction and elliptic degree) of the output light of an FDFA amplifier will not not change or the change is sufficiently small. In this state, a polarization state adjusting optical element adjusts the polarization state of the laser beam coming into a wavelength conversion optical system so that the wavelength conversion optical system has the maximum conversion efficiency. Thus, it is possible to provide an FDFA having a small change of the polarization state of the output light even if the pump light intensity is changed.

TECHNICAL FIELD

The present invention relates to an optical fiber amplifier and a lightsource device, and an exposure device, an object inspection device, anda processing device using the light source device.

BACKGROUND ART

In recent years, a laser beam has been used for various applications,for example, for cutting or processing a metal, a light source of aphotolithography device of a semiconductor manufacturing device, variousmeasuring devices, and operating and treatment devices for surgery,opthalmology, and dentistry.

When a solid-state laser (cited as a concept including semiconductorlaser (or diode laser) in this specification) is used as a laser lightsource, the wavelength of a laser beam emitted from the solid-statelaser is in the visible to infrared region. A method of directlygenerating an ultraviolet light has not been established. For example,the wavelength is too long to be suitable for use in an inspectiondevice. A method of converting such long-wavelength light emitted fromthe solid-state laser to a short-wavelength deep ultraviolet light (forexample, the eighth harmonic; a wavelength of 193 nm) using a nonlinearoptical crystal has been developed and has been described in JapanesePatent Application Laid-Open (JP-A) No. 2001-353176 (Patent Document 1).As nonlinear optical crystals used for such an object, a BBO crystal, anLBO crystal, and a CLBO crystal have been known.

In such laser light source, typically, a laser beam generated from aDFB-LD is amplified using a plurality of optical fiber amplifiers (forexample, EDFAs) and is then converted to the deep ultraviolet light bythe wavelength conversion optical system.

Patent Document 1: JP-A No. 2001-353176

To maintain the intensity of the output laser beam at a target value, insuch a laser light source, feedback control is typically performed. FIG.7 illustrates the overview of such light source device. An output lightfrom a DFB-LD1 comes into an optical fiber amplifier 3 and is thenamplified. The light passes through a polarization state adjustingoptical element 4 having a wavelength plate to come into a wavelengthconversion optical system 5. The light is wavelength converted to alight having a target wavelength.

The polarization state adjusting optical element 4 adjusts thepolarization state of the laser beam coming into the wavelengthconversion optical system 5 in such a way that the wavelength conversionoptical system 5 has the maximum conversion efficiency. For example, thepolarization ellipticity is adjusted by a ¼ wavelength plate. Thepolarization direction is adjusted by a ½ wavelength plate.

A portion of the output light from the wavelength conversion opticalsystem 5 (for example, the light which has a wavelength of 193 nm and isthe eighth harmonic of the light having a wavelength of 1547 nm from theDFB-LD1) is reflected by a partially reflecting mirror 6 and is thentaken out as a monitor light. An automatic output controller 7manipulates an excitation light source (pump light source) 8 whichsupplies an input to the optical fiber amplifier 3 in such a way thatthe intensity of the monitor light is kept constant. It has been thoughtthat the intensity of the output light from the wavelength conversionoptical system 5 is maintained at a target value by the feedback controlsystem.

Actually, however, a change in the output light from the wavelengthconversion optical system 5 for an increase or a decrease in the pumplight intensity sometimes greatly differs from that is assumed. Thismeans that the feedback control sometimes does not functionsufficiently. In extreme cases, when the output of the pump light isincreased, the output of the wavelength conversion optical system 5 islowered. This means that the feedback control causes divergence.

The present invention has been made in view of such circumstances andcan provide an optical fiber amplifier in which even if the intensity ofa pump light is changed, a change in the polarization state of an outputlight is small and the feedback control system can functionsufficiently, and a light source device using the same, and an exposuredevice, an object inspection device, and a processing device using thelight source device.

DISCLOSURE OF THE INVENTION

A first means to achieve the above object is an optical fiber amplifier,wherein the polarization state of an input light is adjusted in such away that the polarization state of an output light will not change evenif an amplification factor is changed.

The present inventors have examined in detail the characteristic of theoptical fiber amplifier 3 used for such an object to find thefollowings. When the pump light intensity is changed for thepolarization state of the input light in a certain range, thepolarization state of the output light is significantly changedaccording to it. When the polarization state of the output light of theoptical fiber amplifier 3 is changed, the polarization state of theinput light to the wavelength conversion optical system 5 optimallyadjusted by the polarization state adjusting optical element 4 is alsochanged. As a result, the output of the wavelength conversion opticalsystem 5 is changed due to a cause different from a change in the pumplight intensity (a fluctuation of the efficiency of the wavelengthconversion optical system due to a change of the polarization state).

As a result of further consideration of the present inventors, thefollowings have been found. The change of the polarization state(polarization direction and ellipticity) of the output light caused bythe amplification factor (the pump light intensity) of the optical fiberamplifier varies depending on the polarization state (polarizationdirection and ellipticity) of the input light to the optical fiberamplifier. When the polarization state of the input light to the opticalfiber amplifier is adjusted, a change of the polarization state of theoutput light caused by the amplification factor of the optical fiberamplifier will be eliminated or significantly reduced. Accordingly, thepolarization state of the input light to the optical fiber amplifier canbe adjusted in such a way that a change of the polarization state of theoutput light caused by the change of the amplification factor of theoptical fiber amplifier may be eliminated or significantly reduced.

The description “adjusted in such a way that the polarization state ofan output light will not change” means not only the polarization stateof the output light will not change at all but also the state of thepolarization change is so small that lowering from the optimum value ofthe wavelength conversion efficiency (the value of the conversionefficiency when the polarization state is in the state optimum forwavelength conversion) can be practically ignored. This is commonlyapplied to descriptions in the specification and claims.

A second means to achieve the above object is an optical fiber amplifierincluding a polarization state adjusting optical element which adjuststhe polarization state of an input light in such a way that thepolarization state of an output light will not change even if anamplification factor is changed.

In this means, the polarization state adjusting optical element having awavelength plate is provided, for example. By adjusting the element, thepolarization state of the input light can be adjusted in such a way thatthe polarization state of the output light will not change even if theamplification factor of the optical fiber amplifier is changed.

A third means to achieve the above object is a light source device whichoptically amplifies a laser beam generated from a solid-state laserlight source by an optical fiber amplifier or optical fiber amplifiersand allows the optically amplified light to be incident on a wavelengthconversion optical system to obtain an output light having apredetermined wavelength, including light separation means for takingout a portion of the output light as a monitor light, and a lightintensity adjusting device which manipulates the intensity of anexcitation light supplied to at least one of the optical fiberamplifiers in such a way that the intensity of the monitor light takenout by the light separation means is kept at a target value, wherein theoptical fiber amplifier which changes an amplification factor by theexcitation light whose intensity is manipulated is an optical fiberamplifier of the first means or the second means.

In this means, when the feedback control which allows the output lightof the light source device to have the target intensity is performed,the change of the polarization state of the output light of the opticalfiber amplifier caused by an increase or a decrease of the excitationlight can be small. Thus, the conversion efficiency of the wavelengthconversion optical system can be maintained almost constant, and thestable feedback control is enabled.

A fourth means to achieve the above object is a light source devicewhich optically amplifies a laser beam generated from a laser lightsource by an optical fiber amplifier and allows the optically amplifiedlight to be incident on a wavelength conversion optical system to obtainan output light having a predetermined wavelength, including lightseparation means for taking out a portion of the output light as amonitor light, and a light intensity adjusting device which manipulatesthe intensity of an excitation light supplied to the optical fiberamplifier in such a way that the intensity of the monitor light takenout by the light separation means is kept at a target value, wherein apolarization state adjusting optical element is arranged between thelaser light source and the optical fiber amplifier.

In a fifth means to achieve the above object according to the fourthmeans, the polarization state adjusting optical element includes a ¼wavelength plate and a ½ wavelength plate.

In a sixth means to achieve the above object according to the fourthmeans, a plurality of the optical fiber amplifiers are provided and themonitor light taken out by the light separation means is supplied to atleast one of the plurality of the optical fiber amplifiers.

In a seventh means to achieve the above object according to the fourthmeans, the polarization state adjusting optical element is arrangedbetween the laser light source and the optical fiber amplifier on whicha laser beam emitted from the laser light source is first incident.

An eighth means to achieve the above object is an exposure deviceincluding a light source device as the third means or the fourth means,a mask supporting portion which holds a photomask having a predeterminedexposure pattern, an object holding portion which holds an exposedobject, an illumination optical system which illuminates the photomaskheld by the mask supporting portion with a light emitted from the lightsource device, and a projection optical system which projects the lightfrom the photomask onto the exposed object held by the object holdingportion.

A ninth means to achieve the above object is an object inspection deviceincluding a light source device as the third means or the fourth means,a supporting portion which holds an object, a detector which receives aprojection image of the object for detection, an illumination opticalsystem which illuminates the object held by the supporting portion witha light emitted from the light source device, and a projection opticalsystem which projects the light from the object onto the detector.

A tenth means to achieve the above object is a polymer crystalprocessing device including a light source device as the third means orthe fourth means, an optical system which guides a laser beam emittedfrom the light source device to a polymer crystal as a processed objectand focus the laser beam onto the processed location of the polymercrystal, and a mechanism which changes a relative position of theoptical system and the polymer crystal.

According to the present invention, it is possible to provide an opticalfiber amplifier in which even if the intensity of a pump light ischanged, the change of the polarization state of the output light issmall and the feedback control system can function sufficiently, and alight source device using the same, and an exposure device, an objectinspection device, and a processing device using the light sourcedevice.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the overview of an optical fiberamplifier according to an embodiment of the present invention and alight source device using the same.

FIG. 2 is a diagram illustrating intensity of an excitation light (pumplight) and intensity of an output light of a wavelength conversionoptical system 5 when the polarization state of a light coming into theoptical fiber amplifier is not adjusted and when the polarization stateof the light coming into the optical fiber amplifier 3 is adjusted by amethod of the present invention.

FIG. 3 is a diagram illustrating the overview of an exposure deviceusing the light source device according to an embodiment of the presentinvention.

FIG. 4 is a diagram illustrating the overview of a mask defectinspection device using the light source device according to anembodiment of the present invention.

FIG. 5 is a diagram illustrating the overview of a polymer crystalprocessing device using the light source device according to anembodiment of the present invention.

FIG. 6 is a diagram illustrating an example in which the polymer crystalprocessing device using the light source device according to anembodiment of the present invention is combined with an opticalmicroscope.

FIG. 7 is a diagram illustrating the overview of a laser light sourcedevice in the related art.

EXPLANATIONS OF LETTERS OR NUMERALS

-   1 DFB-LD-   2 polarization state adjusting optical element, amplifier-   3 optical fiber amplifier-   4 polarization state adjusting optical element-   5 wavelength conversion optical system,-   6 partially reflecting mirror-   7 automatic output controller-   8 excitation light source (pump light source)

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described below using thedrawings. FIG. 1 is a diagram illustrating the overview of an opticalfiber amplifier according to an embodiment of the present invention anda light source device using the same. An output light from a DFB-LD1passes through a polarization state adjusting optical element 2 having awavelength plate. The light comes into an optical fiber amplifier 3 andis then amplified. Then the light passes through a polarization stateadjusting optical element 4 having a wavelength plate to come into awavelength conversion optical system 5. The light is wavelengthconverted to a light having a target wavelength.

The polarization state adjusting optical element 4 adjusts thepolarization state of the laser beam coming into the wavelengthconversion optical system 5 in such a way that the wavelength conversionoptical system 5 has the maximum conversion efficiency. For example, thepolarization ellipticity is adjusted by a ¼ wavelength plate. Thepolarization direction is adjusted by a ½ wavelength plate.

A portion of the output light from the wavelength conversion opticalsystem 5 (for example, the light which has a wavelength of 193 nm andwhich is the eighth harmonic of the light having a wavelength of 1547 nmfrom the DFB-LD1) is reflected by a partially reflecting mirror 6 and isthen taken out as a monitor light. An automatic output controller 7manipulates an excitation light source (pump light source) 8 whichsupplies an input to the optical fiber amplifier 3 in such a way thatthe intensity of the monitor light is kept constant. The intensity ofthe output light from the wavelength conversion optical system 5 ismaintained at a target value by the feedback control system.

This embodiment is compared with the light source circuit in the relatedart illustrated in FIG. 7. In this embodiment, the polarization stateadjusting optical element 2 is provided. The polarization stateadjusting optical element 2 has a ½ wavelength plate and a ¼ wavelengthplate and adjusts the polarization direction and ellipticity. Byadjusting the polarization state adjusting optical element 2 in advance,even if the output of the excitation light source (pump light source) 8is changed, the polarization characteristic (polarization direction andellipticity) of the output light of the optical fiber amplifier 3 willnot change or the change is sufficiently small. In this state, thepolarization state adjusting optical element 4 adjusts the polarizationstate of the laser beam coming into the wavelength conversion opticalsystem 5 in such a way that the wavelength conversion optical system 5has the maximum conversion efficiency. Even if the output of theexcitation light source (pump light source) 8 is changed, the conversionefficiency of the wavelength conversion optical system 5 is maintainedin the state close to the maximum, and the feedback control is madestable.

FIG. 2 illustrates the intensity of an excitation light (pump light)(the normalized value on the horizontal axis) and the intensity of thesecond harmonic of the wavelength conversion optical system 5 (thenormalized value on the vertical axis) when the polarization state of alight coming into the optical fiber amplifier 3 is not adjusted (InputPolarization 1) and when the polarization state of the light coming intothe optical fiber amplifier 3 is adjusted by a method of the presentinvention (Input Polarization 2).

When the polarization state of the input light is not adjusted, the rateof a change in the intensity of the second harmonic of the wavelengthconversion optical system 5 due to a change in the intensity of theexcitation light (pump light) is large. Although not illustrated, whenthe intensity of the excitation light (pump light) is increased andexceeds 1, the intensity of the output light of the wavelengthconversion optical system 5 can be lowered. This means that with achange in the intensity of the excitation light (pump light), thepolarization state of the output of the optical fiber amplifier isgreatly changed and that the conversion efficiency of the wavelengthconversion optical system 5 is greatly deviated from the optimum value.

When the polarization state of the light coming into the optical fiberamplifier 3 is adjusted by the method of the present invention, it isfound that a change in the intensity of the output light of thewavelength conversion optical system 5 with respect to a change in theintensity of the excitation light (pump light) is smaller and the systemis made more stable. This means that the polarization state of theoutput light from the optical fiber amplifier is hardly changed with achange in the excitation light (pump light) intensity and that theconversion efficiency of the wavelength conversion optical system 5 ismaintained at the optimum value.

The light can be amplified by a plurality of optical fiber amplifiersbefore coming into the wavelength conversion optical system 5. In thiscase, the polarization state adjusting optical element 2 may be providedbefore the first-stage optical fiber amplifier of the optical fiberamplifiers of which the pump light is changed and be adjusted in such away that the polarization state of the output light of the last-stageoptical fiber amplifier will not change or the change will be minimized.

Various configurations of the wavelength conversion optical system 5 canbe considered and have been known. An example is described in PatentDocument 1 and the illustration and description thereon are omitted.

With reference to FIG. 3, an exposure device 100 which is configuredusing a light source device 10 according to an embodiment of the presentinvention and is used in the photolithography process as one of thesemiconductor manufacturing processes will be described. In principle,the exposure device used in the photolithography process is the same asphotoengraving. A device pattern precisely plotted on a photomask(reticle) is optically projected and transferred onto a semiconductorwafer or a glass substrate onto which a photoresist is applied.

The exposure device 100 has the light source device 10, an illuminationoptical system 102, a mask supporting base 103 which supports aphotomask (reticle) 110, a projection optical system 104, a placing base105 which places and holds a semiconductor wafer 115 as an exposedobject, and a driving device 106 which horizontally moves the placingbase 105. In the exposure device 100, a laser beam output from the lightsource device 10 is input to the illumination optical system 102 havinga plurality of lenses and then passes therethrough to illuminate theentire surface of the photomask 110 supported by the mask supportingbase 103. The light which has illuminated and passed through thephotomask 110 has an image of the device pattern plotted on thephotomask 110. The light illuminates a predetermined position of thesemiconductor wafer 115 placed on the placing base 105 via theprojection optical system 104.

The image of the device pattern of the photomask 110 becomes smaller andis then focused on the semiconductor wafer 115 by the projection opticalsystem 104 for exposure. According to the exposure device, features ofthe ultraviolet light source including compactness, lightweight, and ahigh degree of freedom in arrangement are exploited to obtain theexposure device which is compact and easy to maintain and operate.

A mask defect inspection device configured using the light source device10 according to the present invention will be described below withreference to FIG. 4. The mask defect inspection device opticallyprojects a device pattern precisely plotted on the photomask onto a TDIsensor (Time Delay and Integration), compares a sensor image with apredetermined reference image, and extracts a defect of the pattern fromthe difference. A mask defect inspection device 120 has the light sourcedevice 10, an illumination optical system 112, a mask supporting base113 which supports the photomask 110, a driving device 116 whichhorizontally moves the mask supporting base, a projection optical system114, and a TDI sensor 125.

In the mask defect inspection device 120, a laser beam output from thelight source device 10 is input to the illumination optical system 112having a plurality of lenses, and then passes therethrough to illuminatea predetermined region of the photomask 110 supported by the masksupporting base 113. The light which has illuminated and passed throughthe photomask 110 has an image of the device pattern plotted on thephotomask 110. The light is focused onto a predetermined position of theTDI sensor 125 via the projection optical system 114.

The horizontal moving speed of the mask supporting base 113 issynchronized with the transfer clock of the TDI 125. The object is notlimited to a mask and the device is used also for inspecting a wafer anda liquid crystal panel.

FIG. 5 is a diagram illustrating the overview of a polymer crystalprocessing device using the light source device 10 of the presentinvention.

An ultraviolet short pulse laser beam 139 emitted from the light sourcedevice 10 is focused on and illuminates a polymer crystal 138 placed ina specimen case 136 via a shutter 132, an intensity adjusting element133, an illumination position control mechanism 134, and a focusingoptical system 135. The specimen case 136 is mounted on a stage 137, ismovable in three dimensional directions of the x axis, the y axis, andthe z axis in the x-y-z orthogonal coordinate system, with the opticalaxis direction as the z axis, and is rotatable about the z axis. Thepolymer crystal is processed by the laser beam which is focused on andilluminates the surface of the polymer crystal 138.

When a processed object of a polymer crystal is processed, it isnecessary to check where in the processed object the laser beamilluminates. In many cases, typically, the laser beam is not a visiblelight and cannot be visually observed. Accordingly, it is preferable tocombine the processing device with an optical microscope.

An example is illustrated in FIG. 6. In the optical system illustratedin FIG. 6, a laser beam from an ultraviolet short pulse laser system 141(corresponding to the reference numerals 10 and 132 to 134 in FIG. 5) isfocused on a predetermined point via the focusing optical system 135.The stage 137 has the function described in FIG. 6. The specimen case136 including the polymer crystal 138 is placed on the stage 137. Thevisible light from an illumination light source 142 is reflected by areflection mirror 143 to Koehler illuminate the specimen case 136. Thepolymer crystal 138 is visually observed by eyes 146 via an objectivelens 144 and an eyepiece 145 of the optical microscope. A cross mark isformed in the optical axis position of the optical microscope, and theoptical axis position can be visually observed.

The focal position of the optical microscope (the focusing position,that is, an object plane which is in focus at visual observation) isfixed. The laser beam focused by the focusing optical system 135 isfocused on the optical axis position and the focal position of theoptical microscope. The processed object is placed on the stage 137 toobserve its image by the optical microscope. The laser beam from thelaser system 141 is focused on the position which is in focus and is thecenter of the cross mark. A relative positional relationship between thelaser system 141, the focusing optical system 135, and the opticalmicroscope is fixed. Only the stage 137 can be moved relatively to thefixed system.

Accordingly, processing is performed by moving the stage 137 in such away that the location to be processed is the optical axis position andthe focusing position of the optical microscope. As a result, theprocessing in a desired location and a desired shape can be performed.If processing is to be automatically performed, an automatic focal pointadjusting device is provided in the optical microscope to drive thestage 137 by its instruction, and the stage 137 may be driven in such away that a predetermined portion of the stage 137 is on the optical axisof the optical microscope. Alternatively, after alignment of a referenceposition, the stage 137 may be driven in two dimensions or threedimensions by a servomechanism.

1. An optical fiber amplifier, wherein the polarization state of aninput light is adjusted in such a way that the polarization state of anoutput light will not change even if an amplification factor is changed.2. An optical fiber amplifier, comprising a polarization state adjustingoptical element which adjusts the polarization state of an input lightin such a way that the polarization state of an output light will notchange even if an amplification factor is changed.
 3. A light sourcedevice which optically amplifies a laser beam generated from a laserlight source by an optical fiber amplifier or optical fiber amplifiersand allows the optically amplified light to be incident on a wavelengthconversion optical system to obtain an output light having apredetermined wavelength, comprising light separation means for takingout a portion of the output light as a monitor light, and a lightintensity adjusting device which manipulates the intensity of anexcitation light supplied to at least one of the optical fiberamplifiers in such a way that the intensity of the monitor light takenout by the light separation means is kept at a target value, wherein theoptical fiber amplifier of which an amplification factor is changed bythe excitation light whose intensity is manipulated is an optical fiberamplifier according to claim
 1. 4. A light source device which opticallyamplifies a laser beam generated from a laser light source by an opticalfiber amplifier and allows the optically amplified light to be incidenton a wavelength conversion optical system to obtain an output lighthaving a predetermined wavelength, comprising light separation means fortaking out a portion of the output light as a monitor light, and a lightintensity adjusting device which manipulates the intensity of anexcitation light supplied to the optical fiber amplifier in such a waythat the intensity of the monitor light taken out by the lightseparation means is kept at a target value, wherein a polarization stateadjusting optical element is arranged between the laser light source andthe optical fiber amplifier.
 5. The light source device according toclaim 4, wherein the polarization state adjusting optical element has a¼ wavelength plate and a ½ wavelength plate.
 6. The light source deviceaccording to claim 4, wherein a plurality of optical fiber amplifiersare provided and the monitor light taken out by the light separationmeans is supplied to at least one of the plurality of the optical fiberamplifiers.
 7. The light source device according to claim 4, wherein thepolarization state adjusting optical element is arranged between thelaser light source and the optical fiber amplifier on which a laser beamemitted from the laser light source is first incident.
 8. An exposuredevice comprising a light source device according to claim 3, a masksupporting portion which holds a photomask having a predeterminedexposure pattern, an object holding portion which holds an exposedobject, an illumination optical system which illuminates the photomaskheld by the mask supporting portion with a light emitted from the lightsource device, and a projection optical system which projects the lightfrom the photomask onto the exposed object held by the object holdingportion.
 9. An exposure device comprising a light source deviceaccording to claim 4, a mask supporting portion which holds a photomaskhaving a predetermined exposure pattern, an object holding portion whichholds an exposed object, an illumination optical system whichilluminates the photomask held by the mask supporting portion with alight emitted from the light source device, and a projection opticalsystem which projects the light from the photomask onto the exposedobject held by the object holding portion.
 10. An object inspectiondevice comprising a light source device according to claim 3, asupporting portion which holds an object, a detector which receives aprojection image of the object for detection, an illumination opticalsystem which illuminates the object held by the supporting portion witha light emitted from the light source device, and a projection opticalsystem which projects the light from the object onto the detector. 11.An object inspection device comprising a light source device accordingto claim 4, a supporting portion which holds an object, a detector whichreceives a projection image of the object for detection, an illuminationoptical system which illuminates the object held by the supportingportion with a light emitted from the light source device, and aprojection optical system which projects the light from the object ontothe detector.
 12. A polymer crystal processing device comprising a lightsource device according to claim 3, an optical system which guides alaser beam emitted from the light source device to a polymer crystal asa processed object and focuses the laser beam onto a processed locationof the polymer crystal, and a mechanism which changes a relativeposition of the optical system and the polymer crystal.
 13. A polymercrystal processing device comprising a light source device according toclaim 4, an optical system which guides a laser beam emitted from thelight source device to a polymer crystal as a processed object andfocuses the laser beam onto a processed location of the polymer crystal,and a mechanism which changes a relative position of the optical systemand the polymer crystal.
 14. A light source device which opticallyamplifies a laser beam generated from a laser light source by an opticalfiber amplifier or optical fiber amplifiers and allows the opticallyamplified light to be incident on a wavelength conversion optical systemto obtain an output light having a predetermined wavelength, comprisinglight separation means for taking out a portion of the output light as amonitor light, and a light intensity adjusting device which manipulatesthe intensity of an excitation light supplied to at least one of theoptical fiber amplifiers in such a way that the intensity of the monitorlight taken out by the light separation means is kept at a target value,wherein the optical fiber amplifier of which an amplification factor ischanged by the excitation light whose intensity is manipulated is anoptical fiber amplifier according to claim 2.